Efficient addressing in wireless hart protocol

ABSTRACT

A method of providing a wireless extension to a wired protocol for transferring data to and from a field device operating in a process control environment via a wired connection, wherein the wired protocol and the wireless extension to the wired protocol have at least one protocol layer in common includes associating a unique address consistent with an addressing scheme of the wired protocol with each of a plurality of wireless devices operating in the process control environment and forming a wireless network, such that a data packet is routed between two of the plurality of wireless devices based on the unique address; associating a network identifier with the plurality of wireless devices; forming, for each of the plurality of wireless devices, a global address including the respective unique address and the network identifier in accordance with a second addressing scheme; and providing access to an external host operating outside the wireless network to each of the plurality of wireless devices based on the global address associated with the wireless device specified at the external host.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority to U.S.Provisional Application No. 60/911,795, entitled “Routing, Scheduling,Reliable and Secure Operations in a Wireless Communication Protocol”filed Apr. 3, 2007, the entire disclosure of which is hereby expresslyincorporated herein by reference.

FIELD OF TECHNOLOGY

The present invention relates generally to wireless communications in aprocess control environment and, more particularly, to a wirelessgateway supporting a wireless communication protocol.

BACKGROUND

In the process control industry, it is known to use standardizedcommunication protocols to enable devices made by differentmanufacturers to communicate with one another in an easy to use andimplement manner. One such well known communication standard used in theprocess control industry is the Highway Addressable Remote Transmitter(HART) Communication Foundation protocol, referred to generally as theHART® protocol. Generally speaking, the HART® protocol supports acombined digital and analog signal on a dedicated wire or set of wires,in which on-line process signals (such as control signals, sensormeasurements, etc.) are provided as an analog current signal (e.g.,ranging from 4 to 20 milliamps) and in which other signals, such asdevice data, requests for device data, configuration data, alarm andevent data, etc., are provided as digital signals superimposed ormultiplexed onto the same wire or set of wires as the analog signal.However, the HART protocol currently requires the use of dedicated,hardwired communication lines, resulting in significant wiring needswithin a process plant.

There has been a move, in the past number of years, to incorporatewireless technology into various industries including, in some limitedmanners, the process control industry. However, there are significanthurdles in the process control industry that limit the full scaleincorporation, acceptance and use of wireless technology. In particular,the process control industry requires a completely reliable processcontrol network because loss of signals can result in the loss ofcontrol of a plant, leading to catastrophic consequences, includingexplosions, the release of deadly chemicals or gases, etc. For example,Tapperson et al., U.S. Pat. No. 6,236,334 discloses the use of awireless communications in the process control industry as a secondaryor backup communication path or for use in sending non-critical orredundant communication signals. Moreover, there have been many advancesin the use of wireless communication systems in general that may beapplicable to the process control industry, but which have not yet beenapplied to the process control industry in a manner that allows orprovides a reliable, and in some instances completely wireless,communication network within a process plant. U.S. Patent ApplicationPublication Numbers 2005/0213612, 2006/0029060 and 2006/0029061 forexample disclose various aspects of wireless communication technologyrelated to a general wireless communication system.

Similar to wired communications, wireless communication protocols areexpected to provide efficient, reliable and secure methods of exchanginginformation. Of course, much of the methodology developed to addressthese concerns on wired networks does not apply to wirelesscommunications because of the shared and open nature of the medium.Further, in addition to the typical objectives behind a wiredcommunication protocol, wireless protocols face other requirements withrespect to the issues of interference and co-existence of severalnetworks that use the same part of the radio frequency spectrum.Moreover, some wireless networks operate in the part of the spectrumthat is unlicensed, or open to the public. Therefore, protocolsservicing such networks must be capable of detecting and resolvingissues related to frequency (channel) contention, radio resource sharingand negotiation, etc.

In the process control industry, developers of wireless communicationprotocols face additional challenges, such as achieving backwardcompatibility with wired devices, supporting previous wired versions ofa protocol, providing transition services to devices retrofitted withwireless communicators, and providing routing techniques which canensure both reliability and efficiency. Meanwhile, there remains a widenumber of process control applications in which there are few, if any,in-place measurements. Currently these applications rely on observedmeasurements (e.g. water level is rising) or inspection (e.g. periodmaintenance of air conditioning unit, pump, fan, etc) to discoverabnormal situations. In order to take action, operators frequentlyrequire face-to-face discussions. Many of these applications could begreatly simplified if measurement and control devices were utilized.However, current measurement devices usually require power,communications infrastructure, configuration, and support infrastructurewhich simply is not available.

SUMMARY

A wireless network operating in a process control environment hasseveral network devices, including at least some field devices forperforming measurements or control functions and a gateway, uses anaddressing scheme which provides one or more applications running on anexternal host disposed outside the wireless network with seamless accessto each network device. In some embodiments, the external host usesglobal addresses consistent with a standard addressing scheme such asthe EUI-64 defined by the IEEE. In operation, the network devicesparticipating in the wireless network route data between the networkdevices using a portion of a global address. Additionally oralternatively, the network devices use a short nickname for routinginternal to the wireless network.

In some embodiments, the portion of a global address of each networkdevice is consistent with an addressing scheme of a counterpart wiredprotocol. In these embodiments, the wireless network supports at leastone layer (e.g., the application layer of the OSI-7 model) of the wiredprotocol and in this sense, the wireless network uses a protocol whichis an extension of the wired protocol. The shared addressing scheme ofthe wired protocol and of the wireless protocol may, in turn, allocateseveral bytes to a unique device identity and several bytes to anextended device type code which may be shared between several devices ofa same type and manufactured by the same company.

In some embodiments, the global address further includes a networkidentity code. A network device operating in the wireless network maynot know the network identity code of the wireless network. When routingdata to a host outside the wireless network, the network device mayinternally route a data packet to a wireless gateway using the sharedaddressing scheme of the wired and wireless protocol, and the wirelessgateway may route the data packet further by appending or pre-pendingthe network identity code.

In an embodiment, the wired protocol is the Highway Addressable RemoteTransducer (HART®) protocol. In this embodiment, the network identitycode may be an OUI associated with the Hart Communication Foundation(HCF).

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a wireless network connected to a plantautomation network via a wireless gateway of the present disclosure.

FIG. 2 is a schematic representation of the layers of a wireless HARTprotocol which may be used in the wireless network illustrated in FIG.1.

FIG. 3 is a block diagram illustrating the use of a multiplexer tosupport HART communications with a legacy field device.

FIG. 4 is a block diagram illustrating the use of a wireless HARTadaptor for supporting wireless HART communications with the legacyfield device illustrated in FIG. 2.

FIG. 5 illustrates a specific example of providing wirelesscommunications between field devices in a tank farm and accessing theresulting mesh network from a distributed control system using awireless gateway of the present disclosure.

FIG. 6 is a block diagram illustrating an example of constructing an8-byte address from a 5-byte wireless HART device identifier for use inthe wireless network illustrated in FIG. 1.

FIGS. 7-10 illustrate several example implementations of a wirelessgateway in accordance with various network topologies and pre-existinginstallations.

FIG. 11 is an exemplary start up sequence which a gateway devicediscussed herein may follow.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary network 10 in which a wireless gatewaydescribed herein may be used. In particular, the network 10 may includea plant automation network 12 connected to a wireless communicationnetwork 14. The plant automation network 12 may include one or morestationary workstations 16 and one or more portable workstations 18connected over a communication backbone 20 which may be implementedusing Ethernet, RS-485, Profibus DP, or using other suitablecommunication hardware and protocol. The workstations and otherequipment forming the plant automation network 12 may provide variouscontrol and supervisory functions to plant personnel, including accessto devices in the wireless network 14. The plant automation network 12and the wireless network 14 may be connected via a wireless gateway 22.More specifically, the wireless gateway 22 may be connected to thebackbone 20 in a wired manner via a first (or “host”) interface 23A andmay communicate with the plant automation network 12 using any suitable(e.g., known) communication protocol. The second (or “wireless”)interface 23B of the wireless gateway 22 may support wirelesscommunications with one or several devices operating in the wirelessnetwork 14.

In operation, the wireless gateway 22, which may be implemented in anyother desired manner (e.g., as a standalone device, a card insertableinto an expansion slot of the host workstations 16 or 18, as a part ofthe input/output (10) subsystem of a PLC-based or DCS-based system,etc.), may provide applications that are running on the network 12 withaccess to various devices of the wireless network 14. In someembodiments, the protocols servicing the network 12 and 14 may share oneor more upper layers of the respective protocol stacks, and the wirelessgateway 22 may provide the routing, buffering, and timing services tothe lower layers of the protocol stacks (e.g., address conversion,routing, packet segmentation, prioritization, etc.) while tunneling theshared layer or layers of the protocol stacks. In other cases, thewireless gateway 22 may translate commands between the protocols of thenetworks 12 and 14 which do not share any protocol layers.

In addition to protocol and command conversion, the wireless gateway 22may provide synchronized clocking used by time slots and superframes(sets of communication time slots spaced equally in time) of ascheduling scheme associated with a wireless protocol (referred toherein as a WirelessHART protocol) implemented in the network 14. Inparticular, the gateway 22 may propagate synchronization data throughthe wireless network 14 at predetermined intervals.

In some configurations, the network 10 may include more than onewireless gateway 22 to improve the efficiency and reliability of thenetwork 10. In particular, multiple gateway devices 22 may provideadditional bandwidth for the communication between the wireless network14 and the plant automation network 12, as well as the outside world. Onthe other hand, the gateway 22 device may request bandwidth from theappropriate network service according to the gateway communication needswithin the wireless network 14. A network manager software module 27,which may reside in the wireless gateway 22, may further reassess thenecessary bandwidth while the system is operational. For example, thewireless gateway 22 may receive a request from a host residing outsideof the wireless network 14 to retrieve a large amount of data. Thewireless gateway 22 may then request the network manager 27 to allocateadditional bandwidth to accommodate this transaction. For example, thewireless gateway 22 may issue an appropriate service request. Thewireless gateway 22 may then request the network manager 27 to releasethe bandwidth upon completion of the transaction.

With continued reference to FIG. 1, the wireless network 14 may includeone or more field devices 30-36. In general, process control systems,like those used in chemical, petroleum or other process plants, includefield devices such as valves, valve positioners, switches, sensors(e.g., temperature, pressure and flow rate sensors), pumps, fans, etc.Generally speaking, field devices perform physical control functionswithin the process such as opening or closing valves or takemeasurements of process parameters. In the wireless communicationnetwork 14, field devices 30-36 are producers and consumers of wirelesscommunication packets.

The devices 30-36 may communicate using a wireless communicationprotocol that provides the functionality of a similar wired network,with similar or improved operational performance. In particular, thisprotocol may enable the system to perform process data monitoring,critical data monitoring (with the more stringent performancerequirements), calibration, device status and diagnostic monitoring,field device troubleshooting, commissioning, and supervisory processcontrol. The applications performing these functions, however, typicallyrequire that the protocol supported by the wireless network 14 providefast updates when necessary, move large amounts of data when required,and support network devices which join the wireless network 14, even ifonly temporarily for commissioning and maintenance work.

If desired, the network 14 may include non-wireless devices. Forexample, a field device 38 of FIG. 1 may be a legacy 4-20 mA device anda field device 40 may be a traditional wired HART device. To communicatewithin the network 14, the field devices 38 and 40 may be connected tothe WirelessHART network 14 via a WirelessHART adaptor (WHA) 50 or 50A.Additionally, the WHA 50 may support other communication protocols suchas Foundation® Fieldbus, PROFIBUS, DeviceNet, etc. In these embodiments,the WHA 50 supports protocol translation on a lower layer of theprotocol stack. Additionally, it is contemplated that a single WHA 50may also function as a multiplexer and may support multiple HART ornon-HART devices.

In general, the network manager 27 may be responsible for adapting thewireless network 14 to changing conditions and for schedulingcommunication resources. As network devices join and leave the network,the network manager 27 may update its internal model of the wirelessnetwork 14 and use this information to generate communication schedulesand communication routes. Additionally, the network manager 27 mayconsider the overall performance of the wireless network 14 as well asthe diagnostic information to adapt the wireless network 14 to changesin topology and communication requirements. Once the network manager 27has generated the overall communication schedule, all or respectiveparts of the overall communication schedule may be transferred through aseries of commands from the network manager 27 to the network devices.

To further increase bandwidth and improve reliability, the wirelessgateway 22 may be functionally divided into a virtual gateway 24 and oneor more network access points 25, which may be separate physical devicesin wired communication with the wireless gateway 22. However, while FIG.1 illustrates a wired connection 26 between the physically separatewireless gateway 22 and the access points 25, it will be understood thatthe elements 22-26 may also be provided as an integral device. Becausethe network access points 25 may be physically separated from thewireless gateway 22, the access points 25 may be strategically placed inseveral different locations with respect to the network 14. In additionto increasing the bandwidth, multiple access points 25 can increase theoverall reliability of the network 14 by compensating for a potentiallypoor signal quality at one access point 25 using the other access point25. Having multiple access points 25 also provides redundancy in case ofa failure at one or more of the access points 25.

In addition to allocating bandwidth and otherwise bridging the networks12 and 14, the wireless gateway 22 may perform one or more managerialfunctions in the wireless network 14. As illustrated in FIG. 1, anetwork manager software module 27 and a security manager softwaremodule 28 may be stored in and executed in the wireless gateway 22.Alternatively, the network manager 27 and/or the security manager 28 mayrun on one of the hosts 16 or 18 in the plant automation network 12. Forexample, the network manager 27 may run on the host 16 and the securitymanager 28 may run on the host 18. The network manager 27 may beresponsible for configuration of the network 14, schedulingcommunication between wireless devices, managing routing tablesassociated with the wireless devices, monitoring the overall health ofthe wireless network 14, reporting the health of the wireless network 14to the workstations 16 and 18, as well as other administrative andsupervisory functions. Although a single active network manager 27 maybe sufficient in the wireless network 14, redundant network managers 27may be similarly supported to safeguard the wireless network 14 againstunexpected equipment failures. Meanwhile, the security manager 28 may beresponsible for protecting the wireless network 14 from malicious oraccidental intrusions by unauthorized devices. To this end, the securitymanager 28 may manage authentication codes, verify authorizationinformation supplied by devices attempting to join the wireless network14, update temporary security data such as expiring secret keys, andperform other security functions.

With continued reference to FIG. 1, the wireless network 14 may includeone or more field devices 30-36. In general, process control systems,like those used in chemical, petroleum or other process plants, includesuch field devices as valves, valve positioners, switches, sensors(e.g., temperature, pressure and flow rate sensors), pumps, fans, etc.Field devices perform physical control functions within the process suchas opening or closing valves or take measurements of process parameters.In the wireless communication network 14, field devices 30-36 areproducers and consumers of wireless communication packets.

The devices 30-36 may communicate using a wireless communicationprotocol that provides the functionality of a similar wired network,with similar or improved operational performance. In particular, thisprotocol may enable the system to perform process data monitoring,critical data monitoring (with the more stringent performancerequirements), calibration, device status and diagnostic monitoring,field device troubleshooting, commissioning, and supervisory processcontrol. The applications performing these functions, however, typicallyrequire that the protocol supported by the wireless network 14 providefast updates when necessary, move large amounts of data when required,and support network devices which join the wireless network 14, even ifonly temporarily for commissioning and maintenance work.

In one embodiment, the wireless protocol supporting network devices30-36 of the wireless network 14 is an extension of the known wired HARTprotocol, a widely accepted industry standard, that maintains the simpleworkflow and practices of the wired environment. In this sense, thenetwork devices 30-36 may be considered WirelessHART devices. The sametools used for wired HART devices may be easily adapted to wirelessdevices 30-36 with a simple addition of new device description files. Inthis manner, the wireless protocol may leverage the experience andknowledge gained using the wired HART protocol to minimize training andsimplify maintenance and support. Generally speaking, it may beconvenient to adapt a protocol for wireless use so that mostapplications running on a device do not “notice” the transition from awired network to a wireless network. Clearly, such transparency greatlyreduces the cost of upgrading networks and, more generally, reduces thecost associated with developing and supporting devices that may be usedwith such networks. Some of the additional benefits of a wirelessextension of the well-known HART protocol include access to measurementsthat were difficult or expensive to obtain with wired devices and theability to configure and operate instruments from system software thatcan be installed on laptops, handhelds, workstations, etc. Anotherbenefit is the ability to send diagnostic alerts from wireless devicesback through the communication infrastructure to a centrally locateddiagnostic center. For example, every heat exchanger in a process plantcould be fitted with a WirelessHART device and the end user and suppliercould be alerted when a heat exchanger detects a problem. Yet anotherbenefit is the ability to monitor conditions that present serious healthand safety problems. For example, a WirelessHART device could be placedin flood zones on roads and be used to alert authorities and driversabout water levels. Other benefits include access to a wide range ofdiagnostics alerts and the ability to store trended as well ascalculated values at the WirelessHART devices so that, whencommunications to the device are established, the values can betransferred to a host. In this manner, the WirelessHART protocol canprovide a platform that enables host applications to have wirelessaccess to existing HART-enabled field devices and the WirelessHARTprotocol can support the deployment of battery operated, wireless onlyHART-enabled field devices. The WirelessHART protocol may be used toestablish a wireless communication standard for process applications andmay further extend the application of HART communications and thebenefits that this protocol provides to the process control industry byenhancing the basic HART technology to support wireless processautomation applications.

Referring again to FIG. 1, the field devices 30-36 may be WirelessHARTfield devices, each provided as an integral unit and supporting alllayers of the WirelessHART protocol stack. For example, in the network14, the field device 30 may be a WirelessHART flow meter, the fielddevices 32 may be WirelessHART pressure sensors, the field device 34 maybe a WirelessHART valve positioner, and the field device 36 may aWirelessHART pressure sensor. Importantly, the wireless devices 30-36may support all of the HART features that users have come to expect fromthe wired HART protocol. As one of ordinary skill in the art willappreciate, one of the core strengths of the HART protocol is itsrigorous interoperability requirements. In some embodiments, allWirelessHART equipment includes core mandatory capabilities in order toallow equivalent device types (made by different manufacturers, forexample) to be interchanged without compromising system operation.Furthermore, the WirelessHART protocol is backward compatible to HARTcore technology such as the device description language (DDL). In thepreferred embodiment, all of the WirelessHART devices should support theDDL, which ensures that end users immediately have the tools to beginutilizing the WirelessHART protocol.

If desired, the network 14 may include non-wireless devices. Forexample, a field device 38 of FIG. 1 may be a legacy 4-20 mA device anda field device 40 may be a traditional wired HART device. To communicatewithin the network 14, the field devices 38 and 40 may be connected tothe WirelessHART network 14 via a WirelessHART adaptor (WHA) 50.Additionally, the WHA 50 may support other communication protocols suchas FOUNDATION® Fieldbus, PROFIBUS, DeviceNet, etc. In these embodiments,the WHA 50 supports protocol translation on a lower layer of theprotocol stack. Additionally, it is contemplated that a single WHA 50may also function as a multiplexer and may support multiple HART ornon-HART devices.

Plant personnel may additionally use handheld devices for installation,control, monitoring, and maintenance of network devices. Generallyspeaking, handheld devices are portable equipment that can connectdirectly to the wireless network 14 or through the gateway devices 22 asa host on the plant automation network 12. As illustrated in FIG. 1, aWirelessHART-connected handheld device 55 may communicate directly withthe wireless network 14. When operating with a formed wireless network14, the handheld device 55 may join the network 14 as just anotherWirelessHART field device. When operating with a target network devicethat is not connected to a WirelessHART network, the handheld device 55may operate as a combination of the wireless gateway 22 and the networkmanager 27 by forming its own wireless network with the target networkdevice.

A plant automation network-connected handheld device (not shown) may beused to connect to the plant automation network 12 through knownnetworking technology, such as Wi-Fi. This device communicates with thenetwork devices 30-40 through the wireless gateway 22 in the samefashion as external plant automation servers (not shown) or theworkstations 16 and 18 communicate with the devices 30-40.

Additionally, the wireless network 14 may include a router device 60which is a network device that forwards packets from one network deviceto another network device. A network device that is acting as a routerdevice uses internal routing tables to conduct routing, i.e., to decideto which network device a particular packet should be sent. Standalonerouters such as the router 60 may not be required in those embodimentswhere all of the devices on the wireless network 14 support routing.However, it may be beneficial (e.g. to extend the network, or to savethe power of a field device in the network) to add one or more dedicatedrouters 60 to the network 14.

All of the devices directly connected to the wireless network 14 may bereferred to as network devices. In particular, the wireless fielddevices 30-36, the adapters 50, the routers 60, the gateway devices 22,the access points 25, and the wireless handheld device 55 are, for thepurposes of routing and scheduling, network devices, each of which formsa node of the wireless network 14. In order to provide a very robust andan easily expandable wireless network, all of the devices in a networkmay support routing and each network device may be globally identifiedby a substantially unique address, such as a HART address, for example.The network manager 27 may contain a complete list of network devicesand may assign each device a short, network unique 16-bit (for example)nickname. Additionally, each network device may store informationrelated to update (or “scan”) rates, connection sessions, and deviceresources. In short, each network device maintains up-to-dateinformation related to routing and scheduling within the wirelessnetwork 14. The network manager 27 may communicate this information tonetwork devices whenever new devices join the network or whenever thenetwork manager 27 detects or originates a change in topology orscheduling of the wireless network 14.

Further, each network device may store and maintain a list of neighbordevices that the network device has identified during listeningoperations. Generally speaking, a neighbor of a network device isanother network device of any type potentially capable of establishing aconnection with the network device in accordance with the standardsimposed by a corresponding network. In case of the WirelessHART network14, the connection is a direct wireless connection. However, it will beappreciated that a neighboring device may also be a network deviceconnected to the particular device in a wired manner. As will bediscussed later, network devices may promote their discovery by othernetwork devices through advertisement, or special messages sent outduring designated periods of time. Network devices operatively connectedto the wireless network 14 have one or more neighbors which they maychoose according to the strength of the advertising signal or to someother principle.

In the example illustrated in FIG. 1, each of a pair of network devicesconnected by a direct wireless connection 65 recognizes the other as aneighbor. Thus, network devices of the wireless network 14 may form alarge number of inter-device connections 65. The possibility anddesirability of establishing a direct wireless connection 65 between twonetwork devices is determined by several factors, such as the physicaldistance between the nodes, obstacles between the nodes (devices),signal strength at each of the two nodes, etc. In general, each wirelessconnection 65 is characterized by a large set of parameters related tothe frequency of transmission, the method of access to a radio resource,etc. One of ordinary skill in the art will recognize that, in general,wireless communication protocols may operate on designated frequencies,such as the ones assigned by the Federal Communications Commission (FCC)in the United States, or in the unlicensed part of the radio spectrum(e.g., 2.4 GHz). While the system and method discussed herein may beapplied to a wireless network operating on any designated frequency orrange of frequencies, the example embodiment discussed below relates tothe wireless network 14 operating in the unlicensed, or shared part ofthe radio spectrum. In accordance with this embodiment, the wirelessnetwork 14 may be easily activated and adjusted to operate in aparticular unlicensed frequency range as needed.

With continued reference to FIG. 1, two or more direct wirelessconnections 65 may form a communication path between nodes that cannotform a direct wireless connection 65. For example, the direct wirelessconnection 65A between the WirelessHART hand-held device 55 andWirelessHART device 36, along with the direct wireless connection 65Bbetween the WirelessHART device 36 and the router 60, may form acommunication path between the devices 55 and 60. As discussed ingreater detail below, at least some of the communication paths may bedirected communication paths (i.e., permitting or defining data transferin only one direction between a pair of devices). Meanwhile, theWirelessHART device 36 may directly connect to each of the networkdevices 55, 60, 32, and to the network access points 25A and 25B. Ingeneral, network devices operating in the wireless network 14 mayoriginate data packets, relay data packets sent by other devices, orperform both types of operations. As used herein, the term “end device”refers to a network device that does not relay data packets sent byother devices and term “routing device” refers to a network device thatrelays data packets traveling between other network devices. Of course,a routing device may also originate its own data or in some cases be anend device. One or several end devices and routing devices, along withseveral direct connections 65, may thus form a part of a mesh network.

Because a process plant may have hundreds or even thousands of fielddevices, the wireless network 14 operating in the plant may include alarge number of nodes and, in many cases, an even larger number ofdirect connections 65 between pairs of nodes. As a result, the wirelessnetwork 14 may have a complex mesh topology, and some pairs of devicesthat do not share a direct connection 65 may have to communicate throughmany intermediate hops to perform communications between these devices.Thus, a data packet may sometimes need to travel along many directconnections 65 after leaving a source device but before reaching adestination device, and each direct connection 65 may add a delay to theoverall delivery time of the data packet. Moreover, some of theseintermediate devices may be located at an intersection of manycommunication paths of a mesh network. As such, these devices may beresponsible for relaying a large number of packets originated by manydifferent devices, possibly in addition to originating its own data.Consequently, a relatively busy intermediate device may not forward atransient data packet immediately, and instead may queue the packet fora relatively significant amount of time prior to sending the packet to anext node in the corresponding communication path. When the data packeteventually reaches the destination device, the destination device mayreply with an acknowledgement packet which may also encounter similardelays. During the time the packet travels to the destination device andthe corresponding acknowledgment packet travels back to the originatingdevice from the destination device, the originating node may not knowwhether the data packet has successfully reached the destination device.Moreover, devices may leave the wireless network 14 due to scheduledmaintenance and upgrades or due to unexpected failures, thus changingthe topology of the mesh network and destroying some of thecommunication paths. Similarly, the devices may join the wirelessnetwork 14, adding additional direct connections 65. These and otherchanges to the topology of the wireless network 14 may significantlyimpact data transmissions between pairs of nodes if not processed in anefficient and timely manner.

Importantly, however, the efficiency of delivering data packets maylargely determine the reliability, security, and the overall quality ofplant operations. For example, a data packet including measurementsindicative of an excessive temperature of a reactor should quickly andreliably reach another node, such as the hand-held device 55 or even theworkstation 16, so that the operator or a controller may immediatelytake the appropriate action and address a dangerous condition ifnecessary. To efficiently utilize the available direct wirelessconnections 65 and properly adjust to the frequently changing networktopology, the network manager 27 may maintain a complete network map 68,define a routing scheme that connects at least some pairs of networkdevices 30-50, and communicate the relevant parts of the routing schemeto each network device that participates in the routing scheme.

In particular, the network manager 27 may define a set of directedgraphs including one or more unidirectional communication paths, assigna graph identifier to each defined directed graph, and may communicate arelevant part of each graph definition to each corresponding networkdevice, which may then update the device-specific, locally storedconnection table 69. As explained in more detail below, the networkdevices 30-50 may then route data packets based on the graph identifierincluded in the headers, trailers, etc. of the data packets. If desired,each connection table 69 may only store routing information directlyrelated to the corresponding network device, so that the network devicedoes not know the complete definition of a directed graph which includesthe network device. In other words, the network device may not “see” thenetwork beyond its immediate neighbors and, in this sense, the networkdevice may be unaware of the complete topology of the wireless network14. For example, the router device 60 illustrated in FIG. 1 may store aconnection table 69A, which may only specify the routing informationrelated to the neighboring network devices 32, 36, 50, and 34.Meanwhile, the WHA 50A may store a connection table 69B, whichaccordingly may specify the routing information related to the neighborsof the WHA 50A.

In some cases, the network manager 27 may define duplicate communicationpaths between pairs of network devices to ensure that a data packet maystill reach the destination device along the secondary communicationpath if one of the direct connections 65 of the primary communicationpath becomes unavailable. However, some of the direct connections 65 maybe shared between the primary and the secondary path of a particularpair of network devices. Moreover, the network manager 27 may, in somecases, communicate the entire communication path to be used to a certainnetwork device, which may then originate a data packet and include thecomplete path information in the header or the trailer of the datapacket. Preferably, network devices use this method of routing for datawhich does not have stringent latency requirements. As discussed indetail below, this method (referred to herein as “source routing”) maynot provide the same degree of reliability and flexibility and, ingeneral, may be characterized by longer delivery delays.

Another one of the core requirements of a wireless network protocol (andparticularly of a wireless network operating in an unlicensed frequencyband) is the minimally disruptive coexistence with other equipmentutilizing the same band. Coexistence generally defines the ability ofone system to perform a task in a shared environment in which othersystems can similarly perform their tasks while conforming to the sameset of rules or to a different (and possibly unknown) set of rules. Onerequirement of coexistence in a wireless environment is the ability ofthe protocol to maintain communication while interference is present inthe environment. Another requirement is that the protocol should causeas little interference and disruption as possible with respect to othercommunication systems.

In other words, the problem of coexistence of a wireless system with thesurrounding wireless environment has two general aspects. The firstaspect of coexistence is the manner in which the system affects othersystems. For example, an operator or developer of the particular systemmay ask what impact the transmitted signal of one transmitter has onother radio system operating in proximity to the particular system. Morespecifically, the operator may ask whether the transmitter disruptscommunication of some other wireless device every time the transmitterturns on or whether the transmitter spends excessive time on the aireffectively “hogging” the bandwidth. Ideally, each transmitter should bea “silent neighbor” that no other transmitter notices. While this idealcharacteristic is rarely, if ever, attainable, a wireless system thatcreates a coexistence environment in which other wireless communicationsystems may operate reasonably well may be called a “good neighbor.” Thesecond aspect of coexistence of a wireless system is the ability of thesystem to operate reasonably well in the presence of other systems orwireless signal sources. In particular, the robustness of a wirelesssystem may depend on how well the wireless system prevents interferenceat the receivers, on whether the receivers easily overload due toproximate sources of RF energy, on how well the receivers tolerate anoccasional bit loss, and similar factors. In some industries, includingthe process control industry, there are a number of important potentialapplications in which the loss of data is frequently not allowable. Awireless system capable of providing reliable communications in a noisyor dynamic radio environment may be called a “tolerant neighbor.”

Effective coexistence (i.e., being a good neighbor and a tolerantneighbor) relies in part on effectively employing three aspects offreedom: time, frequency and distance. Communication can be successfulwhen it occurs 1) at a time when the interference source (or othercommunication system) is quiet; 2) at a different frequency than theinterference signal; or 3) at a location sufficiently removed from theinterference source. While a single one of these factors could be usedto provide a communication scheme in the shared part of the radiospectrum, a combination of two or all three of these factors can providea high degree of reliability, security and speed.

Still referring to FIG. 1, the network manager 27 or another applicationor service running on the network 14 or 12 may define a master networkschedule 67 for the wireless communication network 14 in view of thefactors discussed above. The master network schedule 67 may specify theallocation of resources such as time segments and radio frequencies tothe network devices 25 and 30-55. In particular, the master networkschedule 67 may specify when each of the network devices 25 and 30-55transmits process data, routes data on behalf of other network devices,listens to management data propagated from the network manager 27, andtransmits advertisement data for the benefit of devices wishing to jointhe wireless network 14. To allocate the radio resources in an efficientmanner, the network manager 27 may define and update the master networkschedule 67 in view of the topology of the wireless network 14. Morespecifically, the network manager 27 may allocate the availableresources to each of the nodes of the wireless network 14 (i.e.,wireless devices 30-36, 50, and 60) according to the direct wirelessconnections 65 identified at each node. In this sense, the networkmanager 27 may define and maintain the network schedule 67 in view ofboth the transmission requirements and of the routing possibilities ateach node.

The master network schedule 67 may partition the available radio sourcesinto individual communication channels, and further measure transmissionand reception opportunities on each channel in such units as TimeDivision Multiple Access (TDMA) communication timeslots, for example. Inparticular, the wireless network 14 may operate within a certainfrequency band which, in most cases, may be safely associated withseveral distinct carrier frequencies, so that communications at onefrequency may occur at the same time as communications at anotherfrequency within the band. One of ordinary skill in the art willappreciate that carrier frequencies in a typical application (e.g.,public radio) are sufficiently spaced apart to prevent interferencebetween the adjacent carrier frequencies. For example, in the 2.4 GHzband, IEEE assigns frequency 2.455 to channel number 21 and frequency2.460 to channel number 22, thus allowing the spacing of 5 KHz betweentwo adjacent segments of the 2.4 GHz band. The master network schedule67 may thus associate each communication channel with a distinct carrierfrequency, which may be the center frequency in a particular segment ofthe band.

Meanwhile, as typically used in the industries utilizing TDMAtechnology, the term “timeslot” refers to a segment of a specificduration into which a larger period of time is divided to provide acontrolled method of sharing. For example, a second may be divided into10 equal 100 millisecond timeslots. Although the master network schedule67 preferably allocates resources as timeslots of a single fixedduration, it is also possible to vary the duration of the timeslots,provided that each relevant node of the wireless network 14 is properlynotified of the change. To continue with the example definition of ten100-millisecond timeslots, two devices may exchange data every second,with one device transmitting during the first 100 ms period of eachsecond (i.e., the first timeslot), the other device transmitting duringthe fourth 100 ms period of each second (i.e., the fourth timeslot), andwith the remaining timeslots being unoccupied. Thus, a node on thewireless network 14 may identify the scheduled transmission or receptionopportunity by the frequency of transmission and the timeslot duringwhich the corresponding device may transmit or receive data.

As part of defining an efficient and reliable network schedule 67, thenetwork manager 27 may logically organize timeslots into cyclicallyrepeating sets, or superframes. As used herein, a superframe may be moreprecisely understood as a series of equal superframe cycles, eachsuperframe cycle corresponding to a logical grouping of several adjacenttime slots forming a contiguous segment of time. The number of timeslots in a given superframe defines the length of the superframe anddetermines how often each time slot repeats. In other words, the lengthof a superframe, multiplied by the duration of a single timeslot,specifies the duration of a superframe cycle. Additionally, thetimeslots within each frame cycle may be sequentially numbered forconvenience. To take one specific example, the network manager 27 mayfix the duration of a timeslot at 10 milliseconds and may define asuperframe of length 100 to generate a one-second frame cycle (i.e., 10milliseconds multiplied by 100). In a zero-based numbering scheme, thisexample superframe may include timeslots numbered 0, 1, . . . 99.

As discussed in greater detail below, the network manager 27 reduceslatency and otherwise optimizes data transmissions by including multipleconcurrent superframes of different sizes in the network schedule 67.Moreover, some or all of the superframes of the network schedule 67 mayspan multiple channels, or carrier frequencies. Thus, the master networkschedule 67 may specify the association between each timeslot of eachsuperframe and one of the available channels.

Thus, the master network schedule 67 may correspond to an aggregation ofindividual device schedules. For example, a network device, such as thevalve positioner 34, may have an individual device schedule 67A. Thedevice schedule 67A may include only the information relevant to thecorresponding network device 34. Similarly, the router device 60 mayhave an individual device schedule 67B. Accordingly, the network device34 may transmit and receive data according to the device schedule 67Awithout knowing the schedules of other network devices such as theschedule 69B of the device 60. To this end, the network manager 27 maymanage both the overall network schedule 67 and each of the individualdevice schedules 67 (e.g., 67A and 67B) and communicate the individualdevice schedules 67 to the corresponding devices when necessary. Ofcourse the device schedules 67A and 67B are subsets of and are derivedfrom the overall or master network schedule 67. In other embodiments,the individual network devices 25 and 35-50 may at least partiallydefine or negotiate the device schedules 67 and report these schedulesto the network manager 27. According to this embodiment, the networkmanager 27 may assemble the network schedule 67 from the received deviceschedules 67 while checking for resource contention and resolvingpotential conflicts.

The communication protocol supporting the wireless network 14 generallydescribed above is referred to herein as the WirelessHART protocol 70,and the operation of this protocol is discussed in more detail withrespect to FIG. 2. As will be understood, each of the direct wirelessconnections 65 may transfer data according to the physical and logicalrequirements of the WirelessHART protocol 70. Meanwhile, theWirelessHART protocol 70 may efficiently support communications withintimeslots and on the carrier frequencies associated with the superframesdefined by the device-specific schedules 69.

FIG. 2 schematically illustrates the layers of one example embodiment ofthe WirelessHART protocol 70, approximately aligned with the layers ofthe well-known ISO/OSI 7-layer model for communications protocols. Byway of comparison, FIG. 2 additionally illustrates the layers of theexisting “wired” HART protocol 72. It will be appreciated that theWirelessHART protocol 70 need not necessarily have a wired counterpart.However, as will be discussed in detail below, the WirelessHART protocol70 can significantly improve the convenience of its implementation bysharing one or more upper layers of the protocol stack with an existingprotocol. As indicated above, the WirelessHART protocol 70 may providethe same or greater degree of reliability and security as the wiredprotocol 72 servicing a similar network. At the same time, byeliminating the need to install wires, the WirelessHART protocol 70 mayoffer several important advantages, such as the reduction of costassociated with installing network devices, for example. It will be alsoappreciated that although FIG. 2 presents the WirelessHART protocol 70as a wireless counterpart of the HART protocol 72, this particularcorrespondence is provided herein by way of example only. In otherpossible embodiments, one or more layers of the WirelessHART protocol 70may correspond to other protocols or, as mentioned above, theWirelessHART protocol 70 may not share even the uppermost applicationlayer with any existing protocols.

As illustrated in FIG. 2, the wireless expansion of HART technology mayadd at least one new physical layer (e.g., the IEEE 802.15.4 radiostandard) and two data-link layers (e.g., wired and wireless mesh) tothe known wired HART implementation. In general, the WirelessHARTprotocol 70 may be a secure, wireless mesh networking technologyoperating in the 2.4 GHz ISM radio band (block 74). In one embodiment,the WirelessHART protocol 70 may utilize IEEE 802.15.4b compatibledirect sequence spread spectrum (DSSS) radios with channel hopping on atransaction by transaction basis. This WirelessHART communication may bearbitrated using TDMA to schedule link activity (block 76). As such, allcommunications are preferably performed within a designated time slot.One or more source and one or more destination devices may be scheduledto communicate in a given slot, and each slot may be dedicated tocommunication from a single source device, or the source devices may bescheduled to communicate using a CSMA/CA-like shared communicationaccess mode. Source devices may send messages to one ore more specifictarget devices or may broadcast messages to all of the destinationdevices assigned to a slot.

Because the WirelessHART protocol 70 described herein allows deploymentof mesh topologies, a significant network layer 78 may be specified aswell. In particular, the network layer 78 may enable establishing directwireless connections 65 between individual devices and routing databetween a particular node of the wireless network 14 (e.g., the device34) and the gateway 22 via one or more intermediate hops. In someembodiments, pairs of network devices 30-50 may establish communicationpaths including one or several hops while in other embodiments, all datamay travel either upstream to the wireless gateway 22 or downstream fromthe wireless gateway 22 to a particular node.

To enhance reliability, the WirelessHART protocol 70 may combine TDMAwith a method of associating multiple radio frequencies with a singlecommunication resource, e.g., channel hopping. Channel hopping providesfrequency diversity which minimizes interference and reduces multi-pathfading effects. In particular, the data link 76 may create anassociation between a single superframe and multiple carrier frequencieswhich the data link layer 76 cycles through in a controlled andpredefined manner. For example, the available frequency band of aparticular instance of the WirelessHART network 14 may have carrierfrequencies F₁, F₂, . . . F_(n). A relative frame R of a superframe Smay be scheduled to occur at a frequency F₁ in the cycle C_(n), at afrequency F₅ in the following cycle C_(n+1), at a frequency F₂ in thecycle C_(n+2), and so on. The network manager 27 may configure therelevant network devices with this information so that the networkdevices communicating in the superframe S may adjust the frequency oftransmission or reception according to the current cycle of thesuperframe S.

The data link layer 76 of the WirelessHART protocol 70 may offer anadditional feature of channel blacklisting, which restricts the use ofcertain channels in the radio band by the network devices. The networkmanager 27 may blacklist a radio channel in response to detectingexcessive interference or other problems on the channel. Further,operators or network administrators may blacklist channels in order toprotect a wireless service that uses a fixed portion of the radio bandthat would otherwise be shared with the WirelessHART network 14. In someembodiments, the WirelessHART protocol 70 controls blacklisting on asuperframe basis so that each superframe has a separate blacklist ofprohibited channels.

In one embodiment, the network manager 27 is responsible for allocating,assigning, and adjusting time slot resources associated with the datalink layer 76. If a single instance of the network manager 27 supportsmultiple WirelessHART networks 14, the network manager 27 may create anoverall schedule for each instance of the WirelessHART network 14. Theschedule may be organized into superframes containing time slotsnumbered relative to the start of the superframe. Additionally, thenetwork manager 27 may maintain a global absolute slot count which mayreflect the total of number of time slots scheduled since the start-upof the WirelessHART network 14. This absolute slot count may be used forsynchronization purposes.

The WirelessHART protocol 70 may further define links or link objects inorder to logically unite scheduling and routing. In particular, a linkmay be associated with a specific network device, a specific superframe,a relative slot number, one or more link options (transmit, receive,shared), and a link type (normal, advertising, discovery). Asillustrated in FIG. 2, the data link layer 76 may be frequency-agile.More specifically, a channel offset may be used to calculate thespecific radio frequency used to perform communications. The networkmanager 27 may define a set of links in view of the communicationrequirements at each network device. Each network device may then beconfigured with the defined set of links. The defined set of links maydetermine when the network device needs to wake up, and whether thenetwork device should transmit, receive, or both transmit/receive uponwaking up.

With continued reference to FIG. 2, the transport layer 80 of theWirelessHART protocol 70 allows efficient, best-effort communication andreliable, end-to-end acknowledged communications. As one skilled in theart will recognize, best-effort communications allow devices to senddata packets without an end-to-end acknowledgement and no guarantee ofdata ordering at the destination device. User Datagram Protocol (UDP) isone well-known example of this communication strategy. In the processcontrol industry, this method may be useful for publishing process data.In particular, because devices propagate process data periodically,end-to-end acknowledgements and retries have limited utility, especiallyconsidering that new data is generated on a regular basis. In contrast,reliable communications allow devices to send acknowledgement packets.In addition to guaranteeing data delivery, the transport layer 80 mayorder packets sent between network devices. This approach may bepreferable for request/response traffic or when transmitting eventnotifications. When the reliable mode of the transport layer 80 is used,the communication may become synchronous.

Reliable transactions may be modeled as a master issuing a requestpacket and one or more slaves replying with a response packet. Forexample, the master may generate a certain request and can broadcast therequest to the entire network. In some embodiments, the network manager27 may use reliable broadcast to tell each network device in theWirelessHART network 14 to activate a new superframe. Alternatively, afield device such as the sensor 30 may generate a packet and propagatethe request to another field device such as to the portable HARTcommunicator 55. As another example, an alarm or event generated by thefield device 34 may be transmitted as a request directed to the wirelessgateway 22. In response to successfully receiving this request, thewireless gateway 22 may generate a response packet and send the responsepacket to the device 34, acknowledging receipt of the alarm or eventnotification.

Referring again to FIG. 2, the session layer 82 may providesession-based communications between network devices. End-to-endcommunications may be managed on the network layer by sessions. Anetwork device may have more than one session defined for a given peernetwork device. If desired, almost all network devices may have at leasttwo sessions established with the network manager 27: one for pairwisecommunication and one for network broadcast communication from thenetwork manager 27. Further, all network devices may have a gatewaysession key. The sessions may be distinguished by the network deviceaddresses assigned to them. Each network device may keep track ofsecurity information (encryption keys, nonce counters) and transportinformation (reliable transport sequence numbers, retry counters, etc.)for each session in which the device participates.

Finally, both the WirelessHART protocol 70 and the wired HART protocol72 may support a common HART application layer 84. The application layerof the WirelessHART protocol 70 may additionally include a sub-layer 86supporting auto-segmented transfer of large data sets. By sharing theapplication layer 84, the protocols 70 and 72 allow for a commonencapsulation of HART commands and data and eliminate the need forprotocol translation in the uppermost layer of the protocol stack.

FIGS. 3 and 4 illustrate some of the advantages of a wireless HARTapproach to building or extending process control networks. Inparticular, FIG. 3 contrasts a legacy approach to reporting processvariables schematically represented in configuration 100 to a wired HARTapproach represented in a configuration 102. FIG. 4 further illustratessome of the additional advantages of an approach using a wirelessextension of HART.

Referring to FIG. 3, a hardwired 4-20 mA instrument 102, which may be aCoriolis flowmeter, can only report a single process variable to aDistributed Control System (DCS) 104 via a wired connection 106 whichtypically passes through a marshalling cabinet 108. For example, theinstrument 102 may report a flow rate measurement to the DCS 104. Withthe introduction of the HART standard, it became possible to reportmultiple variables over a single pair of electrical wires and, moreover,the introduction of a HART multiplexer 110 provided support for 4-20 mAdevices. In particular, each of several inputs of the HART multiplexer110 may be used for a separate hardwired connection 112 to a separateloop for measuring flow rate, density, temperature, etc. The HARTmultiplexer 110 may then report these multiple variables to the DCS 104via a wired connection 114. However, while an input module or amultiplexing device such as the HART multiplexer 110 may allow the DCS104 to communicate with several legacy field devices using a singleconnection 112, retrofitting such legacy equipment may be difficult,expensive, and time consuming. To take one example, the use of the HARTmultiplexer 110 still requires re-wiring of the marshalling cabinet 108and adding a hardwired connection 112 for each loop.

On the other hand, FIG. 4 illustrates a more advantageous configuration120 which may rely on the wireless HART protocol 70. As brieflyindicated above, a wireless HART adapter 50 may work in cooperation withan existing instrument (e.g., positioner, transmitter, etc.) to supportthe 4-20 mA signaling standard while providing access to the set ofprocess variables consistent with the HART standard. Thus, theconfiguration 110 may be updated to the configuration 120 while leavingthe marshalling cabinet 108 intact. More specifically, the wireless HARTadaptor 50 may connect to the field device 102 in a wired manner andestablish a wireless connection with a gateway 122, which may alsocommunicate with one or more wireless HART devices 124. Thus, wirelessHART field devices, adapters, and gateways may allow plant operators toupgrade an existing network in a cost-effective manner (i.e., add awireless HART adapter to a legacy device) as well as extend an existingnetwork by using wireless HART devices such as the device 124 in thesame network as wired HART devices (not shown) and legacy devices suchas 4-20 mA equipment. Of course, wired plant automation networks mayalso include devices using other protocols such as Foundation Fieldbus,Profibus DP, etc., and it will be noted that the components 50 and 122may similarly extend and upgrade other networks. For the sake ofclarity, all such networks are referred to herein as “legacy networks.”

It will be also noted that instruments with built-in wireless HARTcapability provide the additional advantage that these devices could beself-powered (e.g., battery-powered, solar powered, etc.). Among otheradvantages of the wireless approach are the ability to add multivariabledata access to individual instruments as required, the elimination ofthe need to re-wire marshalling cabinets to accommodate HARTmultiplexers, and the possibility of maintaining primary measurements ona 4-20 mA signaling line while accessing secondary process measurementsvia the wireless HART adapter 50. Further, a host such as theworkstation 16 (see FIG. 1) may use standard HART commands to read thenecessary process values (universal commands) from a network devicewirelessly coupled to the wireless HART network 14. Still further, auser can access all the device functions available via the HARTcommands, including for example, diagnostic messages, or remotely uploadand download device configuration.

FIG. 5 provides a specific example of forming a wireless mesh network ina tank farm 130 to further illustrate an application of the wirelessgateway described herein. In this particular example, the tank farm 130may utilize several WirelessHART devices for level monitoring. Morespecifically, the tank farm 130 contains several tanks 132 as part of anexisting installation. One of ordinary skill in the art will appreciatethat in order to add gauging or monitoring capability to the tank farm130 and to make every tank 132 visible to a DCS 134, the currently knownsolutions require running cables to each tank to connect newly installedmeters or sensors. Without sufficient spare capacity within the existingcable runs, this operation may be an expensive and time-consumingoption. On the other hand, the wireless solution described herein couldutilize self-powered instruments to report the new process measurements.These measurements could come, for example, from wireless contacttemperature monitoring devices 136 which are simple to fit. Moreover,because the engineers, technicians, and other plant operators servicingthe tank farm 130 would not need to run cables or purchase and installcontroller input modules, the resulting cost saving could make iteconomically viable to add several process measurement points to improveprocess visibility. For example, plant operators may additionally addpressure sensors 138 to each tank. The pressure sensors 138, thewireless contact temperature monitoring devices 136, a wireless gateway137, and additional wireless devices not shown in FIG. 5 may thus form awireless network 140.

As generally discussed above in reference to FIG. 1, it is important toconsider the location of the wireless devices on each tank 132 so thatthe wireless network 140 can form an efficient and reliable mesharrangement. In some cases, it may be necessary to add routers 60 inthose locations where plant equipment could block or seriously affect awireless connection. Thus, in this and in similar situations, it isdesirable that the wireless network 140 be “self-healing,” i.e., capableof automatically addressing at least some of the delivery failures. Tomeet this and other design requirements, the wireless network 140 maydefine redundant paths and schedules so that in response to detecting afailure of one or more direct wireless connections 65, the network 14may route data via an alternate route. Moreover, the paths may be addedand deleted without shutting down or restarting the wireless network140. Because some of the obstructions or interference sources in manyindustrial environments may be temporary or mobile, the wireless network140 may be capable of automatically reorganizing itself. Morespecifically, in response to one or more predetermined conditions, pairsof field devices may recognize each other as neighbors and thus create adirect wireless connection 65 or, conversely, dissolve previously directwireless connections 65. The network manager 142 (illustrated in FIG. 5as residing in the wireless gateway 137) may additionally create,delete, or temporarily suspend paths between non-neighboring devices.

Referring back to FIGS. 1, 4, and 5, the convenience of upgrading orextending a legacy network may further improve if the wireless network14 or 140 provides an efficient approach to addressing the participatingnetwork devices. It may be particularly desirable to seamlessly extendan existing addressing scheme of a device to reduce or even eliminatethe need to reconfigure legacy devices. Moreover, such addressing schememay simplify the development of external applications for accessing andmonitoring the wireless network 14 and, in at least some of thecontemplated embodiments, may allow existing applications to access14-20 mA devices, wired HART devices, and wireless HART devices using asingle, uniform, and backward-compatible scheme. FIG. 6 schematicallyillustrates one approach to assigning address information to eachnetwork device 30-55, 136 and 138 which may provide some or all of theadvantages discussed above.

Referring back to FIG. 2, the data link layer 76 of the wireless HARTprotocol 70 may use an 8-byte address 200 which is illustrated in FIG.6. Meanwhile, the network layer 78 may use a unique five-byte identity202 within the wireless HART network 14. In one embodiment, the wirelessHART protocol 70 supports two types of addresses: a two-byte “nickname”204 and the 8-byte IEEE EUI-64™ address 200. A packet associated withthe data link 76, or data-link protocol data unit (DLPDU), may contain adedicated a field indicating whether the address included in the DLPDUis a two-byte nickname 204 or a full 8-byte address 200. In operation,network devices 30-50, 136 and 138 may route data packets within thewireless network 14 or 140 using either one of the two formats.

In one embodiment, the network manager 27 or 142 may assign the two-bytenickname 204 to individual network devices 30-55, 136 and 138 and managethe nicknames 304 during operation of the wireless network 14 or 140.Additionally or alternatively, other entities or network devices mayparticipate in nickname management. The nickname 204 of a particularnetwork device may be unique only locally, i.e., within the network 14or 142 in which the network device operates. In most cases, a nickname204 refers to a specific network device. However, a predefined value,such as 0xFFFF, may correspond to a broadcast address.

Further, the EUI-64 address 200 may include a three-byteOrganizationally Unique Identifier (OUI) 206, assigned by Institute ofElectrical and Electronics Engineers (IEEE), and the five-byte uniqueidentifier 202, controlled by the HART Protocol 70 or wireless HARTprotocol 72. In the case of wireless HART, the full EUI-64 address 200may be constructed using the Hart Communication Foundation (HCF)Organizationally Unique Identifier (OUI) 206 concatenated with the40-bit HART unique identifier 202 as illustrated in FIG. 6.

Meanwhile, the unique identifier 202 may be a concatenation of thetwo-byte expanded device type code 208 and the two-byte deviceidentifier 210. Preferably, the expanded device type code 208 isallocated by an organization responsible for the definition of thewireless HART protocol 70 such as HCF. Preferably, each devicemanufactured with the same device type code 208 has a distinct deviceidentifier 210. Further, because IEEE 802.15.4 requires multi-bytefields to be transmitted LSB first (“little endian”), the wireless HARTprotocol 72 may be compliant with the LSB ordering. Consequently, thelong address 200 is transmitted in the DLPDU starting with the leastsignificant bit (LSB) of the device identifier 210 and ending with theMSB of the HCF OUI 306. In this embodiment, the nickname 204 may alsotransmitted little-endian (LSB first).

The addressing scheme described above in reference to FIG. 6 may providea seamless transition from a wired environment supporting the wired HARTprotocol 72 to an at least partial wireless capability. From theforegoing, it will be appreciated that gradual addition of wireless HARTdevices 30, 32, etc. to a hardwired HART network without drasticallyrebuilding the respective process control environment is possiblebecause of the seamless expansion of the established HART addressingscheme and of a wireless gateway capable of connecting various types ofnetworks to the wireless HART network 14. The wireless gateway 22 or 137may be a wireless HART device configured with a HART device type. Inmore general terms, the wireless gateway 22 or 137 is also a networkdevice on the wireless HART network 14 or 140. On the other hand, thewireless gateway 22 or 137 may provide a Service Access Point (SAP) tothe plant automation network 12. As one skilled in the art willrecognize, Service Access Points generally serve as endpoints or entrypoints to various services or networks. It is therefore contemplatedthat the wireless gateway 22 or 137 may provide buffering and localstorage for large data transfers in addition to tunneling and protocoltranslation.

Importantly, the second interface 23B of the wireless gateway 22 or 137need not be restricted to any particular protocol. For example, anEthernet-to-wireless wireless gateway 22 or 137 may provide abidirectional path between an industrial Ethernet network and thewireless HART network 14, a Wi-Fi-to-wireless wireless gateway 22 or 137may operate on a 802.11a/b/g radio link to similarly connect thewireless network 14 or 140 to a plant network, and a serial-to-wirelesswireless gateway 22 or 137 may enable a connection to plant automationservers and other equipment which supports serial interfaces. Finally,many suppliers of process control equipment provide proprietaryinput/output (I/O) networks and consequently require a proprietaryinterface. In the latter case, the wireless gateway 22 may be providedwith a system-specific, proprietary interface.

FIGS. 7-10, along with FIG. 1, illustrate several embodiments of awireless gateway which may useful in various network topologies and inview of different pre-existing installations and environmentalconditions. In the example illustrated in FIG. 1, the wireless gateway22 may connect the wireless HART network 14 to a plant automationnetwork 12 via Ethernet or other standard protocol. However, thewireless gateway 22 or 127 may also support other types of connections.As illustrated in FIG. 7, for example, a network 300 may include a DCS302 communicatively coupled to the factory backbone 305. A workstation306 may be also coupled to the factory backbone 20 and may provideaccess to the DCS 302 and to the rest of the network 330 to operatorsand plant personnel. Further, the DCS 302 may communicate with a FieldTermination Assembly (FTA) 310 over a set of wires 312 carrying variableDC current in the 4-20 mA range. As one of ordinary skill willrecognize, the FTA 310 mainly serves the purpose of maintaining the samewiring 316 with the legacy 4-20 mA devices 320 while providing a certaindegree of flexibility with respect to the vendor-specific wiring of theDCS 302. Additionally, the FTA 310 may be connected to a multiplexer 324via a signaling link 326. Similar to the multiplexer 110 discussedearlier, the multiplexer 324 may provide signal translation between oneor more inputs and one or more outputs. In this particular example, themultiplexer 324 may be connected to an adaptor 328 which may translateRS232 signaling to RS485 signaling and thus enable the workstation 306to communicate with the multiplexer 324 via a standard RS232 serialport. Finally, another output of the FTA 310 may be connected to awireless gateway 330 via a link 332 which, in turn, may be connected toa wireless HART network 33 including several wireless devices 336.

In one aspect, the wireless gateway 330 operates in the network 300 toseamlessly expand the legacy part of the network 300 including the wiredfield devices 320, the DCS 302, and the multiplexer 324 to includewireless HART devices 336 of the wireless HART network 300. In thisembodiment, the link 326 and 332 between the wireless gateway 330 andthe multiplexer 324 may both support a RS485 connection. Thisarrangement may allow the wireless gateway 330 to handle certain RS485commands and to pass all other commands through to one of the targetfield devices 336 as HART commands.

In another embodiment, a wireless gateway may be provided as part of anew wireless network installation. Referring back to FIG. 1, thewireless gateway 22 may connect to the plant automation network 12. Thenetwork manager 27 and the security manager 28 may run on the wirelessgateway 22 or on a host residing on the network 12, such as theworkstation 16. The wireless gateway 22 may connect to the plantautomation network 12 via any bus such as Profibus DP, for example.

In another embodiment which is also consistent with the illustration inFIG. 1, the gateway 22 may be a standalone unit including both thenetwork manager 27 and the security manager 28. In this embodiment, ahigher level application such as asset management software, for example,may run on the workstation 16 and communicate with the network devices30-50. Also, the handheld wireless HART device 55 may read primary andsecondary process measurements and alarms periodically transmit thisdata via the gateway 27 and over some other network type, such as acellular network for example, to a host application. Alternatively, thishost application may run on the workstation 16 or 18 which maycommunicate with the gateway 22 over the factory bone 20.

Now referring to FIG. 8, a network 360 may include another embodiment ofthe wireless gateway 362. In particular, the wireless gateway 362 may beimplemented as a PC card compatible with an expansion slot of a personalcomputer or workstation 364. In this embodiment, the wireless gateway362 may easily support higher level applications such as assetmanagement software. Also, the primary and secondary measurements,alarms, etc. could also be accessed through the wireless gateway 362operating as a SAP and processed locally or transmitted over some othernetwork to other plant applications.

Finally, FIG. 9 illustrates a configuration 380 in which a wirelessgateway 382 is built into an I/O system 384. Alternatively, the system380 may be a DCS-based system. This configuration may provide I/Omeasurements for monitoring and control applications of the system 380.Additionally, higher level applications such as asset managementapplications running on a host 386 may operate with this particularconfiguration by tunneling HART commands through a control networkresiding on the factory backbone 388 and via the I/O system 384.

FIG. 10 provides a more detailed illustration of an embodiment in whicha wireless gateway is distributed among several network components. Inparticular, a network 390 may include a plant automation network 392coupled to a wireless network 394 via a gateway 396 which includes avirtual gateway 400 residing on a network host 402 and two networkaccess points 404 and 406. In accordance with this embodiment, thegateway 396 may alternatively include a single access point 404 or 406or, conversely, may include more than two access points 404 or 406.Moreover, the gateway 396 may be dynamically expanded with additionalaccess points during operation. In general, the number of access points404 or 406 may depend on such factors as a physical layout of theautomation plant in which the wireless network 394 operates (e.g.,obstacles blocking wireless signals, relative distances between wirelessdevices, etc.), bandwidth requirements of the wireless network 394(e.g., a number of wireless devices transmitting data to a hostoperating in the plant automation network 392, a frequency oftransmissions at each device), as well as the more obvious factors suchas cost and the difficulty of wiring each individual network accesspoints 404 and 406. Preferably but not necessarily, the access points404 and 406 provide at least some redundancy with respect to each otherso that if the network access point 404 fails, for example, the networkaccess point 406 may take over and compensate for at least a part of thelost bandwidth.

In operation, the virtual gateway 400 may communicate with each of thenetwork access points 404 and 406 to establish wireless connections withat least some of the wireless network devices 412-418 operating in thewireless network 394, provide clocking to the wireless network 394 viaor both of network access points 404 and 406, control the allocation ofwireless resources (e.g., timeslots and channels) at each of networkaccess points 404 and 406. Additionally, the virtual gateway 400 may beresponsible for protocol and address translation to ensure seamlessco-operation of the wireless network 394 with the plant automationnetwork 392.

Specifically with respect to addressing, the gateway 396 may increasethe efficiency and reliability of routing of data to and from thewireless network devices 412-418 by assigning a well-known address 420to the virtual gateway 400. Meanwhile, each of the network access points404 and 406 may have a separate address 424 and 426, respectively. Inoperation, the network devices 412-418 may route data to the gateway 396by specifying the well-known address 420. In this sense, the networkdevices 412-418 need not know how many network access points 404 and 406operate as part of the gateway 396 or what addresses are associated witheach of the network access points 404 and 406. Moreover, in someembodiments, each of the network devices 412-418 may have at least onepath (e.g., a direct connection or a connection via one or moreintermediate network devices) to each of network access points 404 and406. In this manner, the entire wireless network 394 may remainaccessible to a host in the network 392 even if all but one of thenetwork access points 404 or 406 fail. In alternative embodiments, thevirtual gateway 400 or the corresponding network manager may add ordelete wireless connections between the network access points 404 or 406and the network devices of the wireless network 394 in response todetecting a change in status of one or more of the network access points404 or 406. For example, the gateway 400 may report a failure of thenetwork access points 404 to the manager which, in turn, may add thedirect connection 430 to create a path between the network 410 and thenetwork access point 406 via the network device 412.

With respect to protocol translation, it will be noted that in general,the wireless gateway 396 may support any protocols running in thenetworks 392 and 394. However, in some embodiments, the gateway 396 mayrecognize the one or more shared layers of the respective protocols andleave the shared one or more upper layers intact when translatingbetween the protocols. In one particularly useful embodiment, thewireless network 394 may operate using the wireless HART protocol 70(see FIG. 2) and the host 402 may originate HART commands to the networkdevices 410-418 via a HART modem, for example. In this case, the gateway396 may perform protocol translation on the layers 74-82 withoutmodifying the data associated with the layer 84.

Referring generally to FIGS. 1, 4, 5, 7, and 8-10, the wireless network14, 140, or 394 may further improve the responsiveness to changingenvironmental conditions and additionally improve the reliability ofinter-device communications by gradually building the wireless networkstarting with a gateway device. Referring back to FIG. 1, the wirelessHART network 14 may initially form from the network manager 27 and thegateway 22. In accordance with the various embodiments discussedearlier, the network manager 27 and the gateway 22 may reside on thesame physical host or may be connected by a bidirectional connection ina wired or wireless manner. More specifically, FIG. 11 illustrates anexample start-up procedure 450 which may run at initialization of thewireless HART network 14.

As illustrated in FIG. 11, the routine 450 may include a first step 452during which the gateway 22 start ups and initializes. In a step 454,the gateway 22 may create an instance of the network manager 27. It willbe noted that while the example step 454 includes the creation of thenetwork manager 27 as a software instance running in the same physicalhost as the gateway 22, the network manager 27 may also run on one ofthe workstations 16 or 18 or may be distributed among several hardwarecomponents. In an alternative embodiment, the network manager 27 maystart first and may create an instance of the virtual gateway 24.

Either the gateway 22 or the network manager 27 may then create aninstance of the security manager 28 in a block 456. During operation ofthe wireless HART network 14, the security manager 28 may work with thenetwork manager 27 to protect the wireless HART network 14 from variousadversarial threats. In particular, the security manager 28 may providesecurity keys to the network manager 27 which may be used for deviceauthentication and encryption of data in the wireless HART network 14.The security manager 28 may generate and manage the cryptographicmaterial used by the wireless HART network 14 and may be alsoresponsible for the generation, storage, and management of these keys.In a block 458, the security manager 28 may establish a connection withthe network manager 27. In subsequent operations, the security manager28 may work closely with the network manager 27 in a server-clientarchitecture. In some embodiments, a single instance of the securitymanager 28 may service more than one wireless HART network 14.

Next, the gateway 22 may start providing clocking, or synchronization ina block 460. Because the wireless HART network 14 may have more than onegateway 22 and because synchronization typically comes from a singlesource, the network manager 27 may explicitly designate the source ofsynchronization. For example, the network manager 27 may designate thenetwork access point 25A as the clocking source. If desired, both of thenetwork access point 25A and network access point 25B of FIG. 1 mayprovide synchronized clocking signals.

With continued reference to FIG. 11, the network manager 27 may create afirst superframe of the wireless HART network 14 and a first networkgraph in a block 462. The wireless HART network 14 may then startadvertising in a block 464 so that field devices 30, 32, etc may processthe advertisement packets and initiate the process of joining thenetwork. As discussed above, the gateway 22 may reside on the wirelessHART network 14 as a network device. Thus, field devices may communicatewith the gateway 22 using the same commands and procedures these devicesuse to communicate with the neighboring field devices. Further, fielddevices may receive and respond to advertisement packets from anynetwork devices, including the gateway 22.

Although the forgoing text sets forth a detailed description of numerousdifferent embodiments, it should be understood that the scope of thepatent is defined by the words of the claims set forth at the end ofthis patent. The detailed description is to be construed as exemplaryonly and does not describe every possible embodiment because describingevery possible embodiment would be impractical, if not impossible.Numerous alternative embodiments could be implemented, using eithercurrent technology or technology developed after the filing date of thispatent, which would still fall within the scope of the claims.

What is claimed:
 1. A method of providing a wireless extension to awired protocol for transferring data to and from a field deviceoperating in a process control environment via a wired connection togenerate a wireless protocol, the method comprising: adding a networklayer and a session layer to the wired protocol to generate the wirelessprotocol, the wireless protocol and the wireless protocol sharing acommon application layer including command oriented, predefined datatypes and application procedures that correspond to a plurality ofwireless devices operating in the process control environment, thewireless protocol and the wired protocol utilized in the process controlenvironment for transferring process control data between field devicescorresponding to the plurality of wireless devices, and the plurality ofwireless devices forming a wireless network; identifying each wirelessdevice of the plurality of wireless devices by a respective uniqueaddress consistent with a first addressing scheme of the wired protocol,wherein a data packet is routed between two of the plurality of wirelessdevices within the wireless network based on the respective uniqueaddress of the each wireless device; associating a network identifier ofthe wireless network with the each wireless device included in theplurality of wireless devices; forming, for the each wireless device ofthe plurality of wireless devices, a global address uniquely identifyingthe each wireless device, the global address including the respectiveunique address and the network identifier of the wireless network inaccordance with a second addressing scheme; and providing access to anexternal host operating outside the wireless network to the eachwireless device included in the plurality of wireless devices based onthe global address associated with the each wireless device specified atthe external host.
 2. The method of claim 1, wherein forming a globaladdress consists of appending an Organizationally Unique Identifier(OUI) allocated by the Institute of Electrical and Electronics Engineers(IEEE) to the respective unique address.
 3. The method of claim 2,wherein appending the OUI is appending the OUI associated with the HART®communication protocol.
 4. The method of claim 1, further comprising:associating the first addressing scheme of the wired protocol with thenetwork layer of the wireless protocol; and associating the secondaddressing scheme with a data link layer of the wireless protocol,wherein the network layer of the wireless protocol is layered over thedata link layer of the wireless protocol.
 5. The method of claim 1,wherein identifying the each wireless device of the plurality ofwireless devices by the respective unique address consistent with thefirst addressing scheme of the wired protocol includes: associating aunique device identifier occupying a first number of bytes with therespective unique address; and associating an expanded device type codeoccupying a second number of bytes with the respective unique address;wherein each device having a same type and a same manufacturer sharesthe same expanded device type code.
 6. The method of claim 5, wherein asum of the first number of bytes and the second number of bytes is fivebytes; wherein the network identifier is a three byte OrganizationallyUnique Identifier (OUI) allocated by the Institute of Electrical andElectronics Engineers (IEEE).
 7. The method of claim 1, wherein theglobal address is consistent with an eight byte Extended UniqueIdentifier (EUI-64) IEEE standard.
 8. The method of claim 1, wherein thefirst addressing scheme of the wired protocol is a HART addressingscheme.
 9. The method of claim 1, further comprising associating anickname with the each of the plurality of wireless network devices,wherein the nickname occupies a smaller number of bytes than therespective unique address consistent with the first addressing scheme ofthe wired protocol, and wherein the each of the plurality of wirelessdevices can route data to at least one the plurality of wireless devicesbased on either the nickname of the at least one the plurality ofwireless devices or the respective unique address of the at least onethe plurality of wireless devices.
 10. A communication network operatingin a process control environment, comprising: a plurality of fielddevices each configured to perform a physical control function withinthe process control environment and to transmit process control datacorresponding to the physical control function; a computing devicecommunicatively coupled to a Distributed Control System (DCS) andconfigured to configure the plurality of field devices; a first fielddevice of the plurality of field devices, the first field device beingconfigured by the computing device, having only a wired connection tothe Distributed Control System (DCS), and supporting a wired protocolfor transferring process control data generated by a respective physicalprocess control function performed by the first field device to a secondfield device and to the computing device; the first device including aunique wired address of the wired protocol for transferring processcontrol data; the second field device of the plurality of field devices,the second field device being configured by the computing device, havinga wireless connection to the DCS, and supporting a wireless protocol fortransferring process control data generated by a respective physicalprocess control function performed by the second field device to thecomputing device and for transferring the process control data to thefirst field device or to another field device supporting the wiredprotocol; the second device including a unique wireless address extendedfrom the wired protocol for transferring process control data, wherein:the wireless protocol comprises a network layer and a session layeradded to the wired protocol, the wireless protocol and the wirelessprotocol share a common application layer including command oriented,predefined data types and application procedures corresponding to theplurality of field devices, and a wired addressing scheme of the wiredprotocol is included in a wireless addressing scheme of the wirelessprotocol at the network layer of the wireless protocol; and a routingdevice transferring data between the first field device and the DCS andbetween the second field device and the DCS based on the unique wiredaddress of the first device associated with the wired protocol and basedon the unique wireless address of the second field device associatedwith the wired protocol.
 11. The communication network of claim 10,wherein the routing device is a Field Termination Assembly (FTA) coupledto the DCS via at least one pair of wires.
 12. The communication networkof claim 11, wherein the DCS propagates data to the FTA via the at leastone pair of wires in accordance with the HART® communication protocol;and wherein the unique wireless address associated with the wiredprotocol is a HART address.
 13. The communication network of claim 10,wherein the second field device further includes a network identifiershared with at least a third field device having a wireless connectionto the DCS.
 14. A method of providing an efficient addressing in awireless mesh network operating in a process control environment, themethod comprising: extending a wired protocol to generate a wirelessprotocol by adding a network layer and a session layer to the wiredprotocol, the wireless protocol and the wireless protocol sharing anapplication layer including command oriented, predefined data types andapplication procedures corresponding to a plurality of wireless devicesparticipating in the wireless mesh network; associating a unique firstaddress including a device identifier and a device type code with eachof the plurality of wireless devices participating in the wireless meshnetwork, the unique first address being consistent with the wiredprotocol; associating a unique second address with the each of theplurality of wireless devices participating in the wireless meshnetwork, the unique second address having a length shorter than a lengthof the unique first address, and the unique second address supported bythe wireless protocol; routing a packet including data between each ofthe plurality of wireless devices and at least one other of theplurality of wireless devices by using the network layer of the wirelessprotocol and based on an indication, included in the packet, of whetherthe unique first address or on the unique second address is included inthe packet; and routing data between each of the plurality of wirelessdevices and a host operating outside the wireless mesh network based ona global address including the unique first address and a constant valueassociated with the wireless mesh network.
 15. The method of claim 14,routing data between each of the plurality of wireless devices and ahost operating outside the wireless mesh network is routing data basedon an address consistent with one of the EUI IEEE standards.
 16. Themethod of claim 14, wherein the wired protocol is HART®.